A vehicle may include a belt integrated starter/generator (BISG) to start an internal combustion engine and to charge a battery. The BISG may also provide torque to the engine when the engine is operating (e.g., combusting fuel and rotating) to boost driveline output. A BISG and its accompanying battery may be sized to provide robust engine starting when the engine stops at a position that requires a larger amount of torque to rotate the engine in a forward direction and to achieve a cranking speed that is sufficient for engine starting during cold ambient conditions. However, such a BISG may not be cost effective for some engine applications. Therefore, it may be desirable to provide a way of starting an engine with a reduced amount of torque so that a smaller BISG and battery may reliably start an engine without having a large excess torque capacity.
The inventors herein have recognized the above-mentioned issues and have developed an engine operating method, comprising: rotating an engine crankshaft in a forward direction when combusting air and fuel in the engine; rotating the engine crankshaft in a reverse direction to a crankshaft position at which a torque to turn the engine exceeds a predetermined output torque of a belt integrated starter/generator (BISG) in response to the engine being stopped; and holding the engine stopped at the crankshaft position via supplying current to the BISG.
By rotating the engine crankshaft in a reverse direction that is opposite a direction that the engine crankshaft rotates when it is combusting fuel, it may be possible to provide the technical result of starting an engine with a BISG and battery that has a lower output torque capacity. In particular, the engine crankshaft may be rotated in a reverse direction and then stopped. Once an engine start request is issued, the BISG may rotate the engine crankshaft in a forward direction to start the engine. The engine crankshaft angular rotational distance at which the engine exerts a higher compression and friction losses when the engine is rotated in the forward direction may be increased by first rotating the engine in a reverse direction. By increasing the crankshaft angular rotational distance before compression and friction losses increase when the engine is rotated, it may be possible for the engine to reach a higher cranking speed. Rotating the engine at a higher cranking speed may allow the engine's inertia to help the BISG rotate the engine trough top-dead-center compression stroke of a cylinder so that the engine may be started with less BISG torque as compared to if the engine stopped near top-dead-center compression stroke of a cylinder.
The present description may provide several advantages. In particular, the approach may improve engine starting robustness. Further, the approach may reduce system cost by enabling robust engine starting via a BISG with lower torque output capacity. In addition, the approach may be implemented in several ways that may help to reduce electrical power consumption.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.